Acas, headed by former TUC general secretary Sir Brendan Barber, offers arbitration between employers and trade unions in industrial disputes.

PCS took a claim to the Central Arbitration Committee in 2016, saying that the organisation had not consulted properly with trade unions over its recent transformation programme, which includes the closure of the Liverpool office.

But Acas challenged the CAC jurisdiction on the issue, saying it was subject to a different set of rules because it was concerned with public duties not economic activities.

That challenge has been rejected now by the Employment Appeal Tribunal, which ruled that the definition of “economic activity” was “equally applicable to services which are funded from another source” as much as services paid for by customers.

Welcoming the judgement, PCS general secretary Mark Serwotka said it was “quite remarkable” that a body with Acas’s brief would seek to avoid consulting its workforce.

He said the ruling showed that “Acas needs to obey the rules on consultation just like any other employer.”

An Acas spokesman said: “Our appeal was in no way avoiding our responsibilities to consult our employees. We have been and remain committed to consulting extensively with our trade unions.

“We appealed against the CAC decision because the issue of whether we primarily carry out public duties or economic activity goes to the heart of Acas’s identity and has implications which are wider than the current issue of consultation.”